Norio Nanjo was a Japanese novelist, screenwriter, and economist born on November 14, 1908, in Tokyo, Japan, who passed away on October 30, 2004. His real name was Koga Hidemasa. A graduate of the Law and Economics departments at Tokyo Imperial University, Nanjo worked as a professor of political science and economics at Kokugakuin University and served as a常务理事 on Japan's Economic Reconstruction Committee. He made his literary debut in 1951 and earned the prestigious Naoki Prize in 1956 for his novel Tōdai Oni. In 1982, he received the Yoshikawa Eiji Literature Prize for another work, Saiko Nikki.

As an original creator, Nanjo is best known to modern anime and manga audiences as the author of the historical novel Suruga-jō Gozen Jiai. Written as a series of short stories, this novel serves as the source material for the manga and anime series Shigurui. Specifically, the manga by Takayuki Yamaguchi is an adaptation of the first chapter of Nanjo's novel. While Nanjo provided the original story and characters for this brutal samurai drama, the manga itself is written and illustrated by Yamaguchi. The work was serialized in Akita Shoten's Champion Red from 2003 to 2010, and the twelve-episode anime adaptation was produced by the studio Madhouse in 2007.

Beyond this singular connection to contemporary anime, Nanjo was a prolific writer of jidaigeki, or period dramas, and many of his other works were adapted into films during the 1960s. Notable film credits based on his stories include Bushidō Zankoku Monogatari, Daisan no Kagemusha, and Shikonmado - Dai tatsumaki, all released in 1963 and 1964. He also wrote the novel Murasaki Ukyonosuke, which was adapted into a popular two-part film series. His work continued to be adapted for television, including the series Genroku Taiheiki in 1975 and two iterations of Tsukikage Hyōgo Abare Tabi in 1989 and 1990.

The recurring themes in Nanjo's writing, which are fully on display in the source material for Shigurui, focus on the brutal and cruel realities of life under the samurai class. His style is known for eschewing romanticized depictions of bushido in favor of a raw, often grotesque examination of violence, hierarchy, and human suffering. A key theme explored in his work, as noted in adaptations of Suruga-jō Gozen Jiai, is the idea that extreme cruelty is born when human emotions are pushed to their limits. This philosophical approach, combined with unflinching depictions of sword fighting and its physical consequences, forms the core of his artistic identity and distinguishes his historical fiction from more traditional tales. His significance to the anime and manga industry lies primarily in providing the foundational narrative for Shigurui, a work known for its uncompromising violence and psychological depth, which has been recognized with a nomination for the Tezuka Osamu Cultural Prize and high rankings on Kono Manga ga Sugoi! lists of top manga.